The present invention relates generally to manufactured seeds and, more particularly, to an end seal for a manufactured seed.
Asexual propagation for plants has been shown for some species to yield large numbers of genetically identical embryos, each having the capacity to develop into a normal plant. Such embryos must usually be further cultured under laboratory conditions until they reach an autotrophic xe2x80x9cseedlingxe2x80x9d state characterized by an ability to produce their own food via photosynthesis, resist desiccation, produce roots able to penetrate soil and fend off soil microorganisms. Some researchers have experimented with the production of the artificial seeds, known as manufactured seeds, in which individual plant somatic or zygotic embryos are encapsulated in a seed coat. Examples of such manufactured seeds are disclosed in U.S. Pat. No. 5,701,699, issued to Carlson et al., the disclosure of which is hereby expressly incorporated by reference.
Typical manufactured seeds include a seed coat, synthetic gameophyte and a plant embryo. The seed coat typically is a cylindrical capsule having a closed end and an open end. The synthetic gameophyte is placed within the seed coat, such that the gameophyte substantially fills the interior of the seed coat. A longitudinally extending hard porous insert, commonly known as a cotyledon restraint, may be centrally located within the synthetic gameophyte and includes a centrally located cavity extending partially through the length of the cotyledon restraint. The cavity is sized to receive the plant embryo therein. The well known plant embryo includes a radicle end and a cotyledon end. The plant embryo is deposited within the cavity of the cotyledon restraint cotyledon end first. The plant embryo is then sealed within the seed coat by at least one end seal. There is a weakened spot in the end seal to allow the radicle end of the embryo to penetrate the end seal.
Typically, the end seal is formed from a sheet of polymer material. In the past, a mechanical rod is used to stretch and, therefore, thin or weaken a small spot in the center of the seal. The weakened spot in the end seal is desirable because as the embryo begins to grow, the weakened spot permits tangential distribution of load to assist in the breakthrough of the embryo through the end seal.
A disk of predetermined diameter is then cut from the polymer sheet with the weakened spot in the center of the disk forming the end seal. After the end seals are cut from the polymer sheet, they are pushed out of a punch cavity with a rod and then fall by gravity on top of the seed coat. The seed coat with the end seal is then transferred to a separate station to heat fuse the end seals to the seed coats. Although such a process is effective at forming and sealing end seals to the seed coat of a manufactured seed, it is not without its problems.
First, it is difficult to maintain the exact location of the opening into the cavities of the cotyledon restraint as the manufactured seed passes through the production line. Second, the placement of the end seal over the seed coat is not reliable. Additionally, the end seals tend to stick to the punch or punch cavity. Further, fusing of the end seals to the seed coats is difficult and time consuming because the end seals must be heated to a point where the end seal is fused to the seed coat without damaging the dome or weakened area itself. Sometimes the fusing process melts holes in the weakened spot. Finally, the fusing process may cause damage to the plant embryo itself. As a result, mass production of manufactured seeds is not only time consuming, but also expensive.
Thus, there exists a need for a method of manufacturing and attaching an end seal to a seed coat of a manufactured seed that can produce and attach a large number of end seals to a manufactured seed at a relatively low cost, a high degree of reliability and without damaging the plant embryo located within the seed coat.
In accordance with the present invention, a method of manufacturing and attaching an end seal to a manufactured seed coat is provided. The method includes the step of positioning a first manufactured seed coat having an opening and a perimeter. The method also includes the step of prestressing an area of a sheet of material. The sheet is positioned on the first manufactured seed to substantially center the area over the manufactured seed coat opening. Finally, the method includes the step of attaching the polymeric sheet to the first manufactured seed coat to seal the manufactured seed coat opening.
In one embodiment, the step of prestressing the area of the sheet includes ablating a predetermined area of the sheet. The predetermined area of the sheet is located according to the location of the opening of the seed coat.
In yet another embodiment of the present invention, the method further includes the step of placing the sheet between first and second templates before ablating the predetermined area of the sheet, the first and second templates each having a bore extending therethrough. The step of ablating the predetermined area of the sheet forms an annular collar on at least one surface of the sheet.
In still yet another embodiment of the present invention, the step of attaching the sheet to the manufactured seed includes fusing the sheet to the manufactured seed to seal the embryo within the manufactured seed.
The present invention is also directed to the resulting manufactured seed that includes a seed coat having a length and a cavity extending from one end of the seed coat partially through the length of the seed coat. The manufactured seed also includes an embryo disposed within the cavity and an end seal attached to one end of the seed coat. The end seal includes an ablated area, wherein the ablated area is located on a predetermined portion of the end seal to position the ablated area substantially over the opening of the cavity.
The method of attaching an end seal to a manufactured seed coat, as well as the resulting manufactured seed, form in accordance with the present invention has several advantages over currently available methods. The present invention is more accurate because it prestresses a predetermined area of the polymeric sheet according to predetermined coordinates of the opening in the manufactured seed coat. Also, the problem of misaligning the end seals with the seed coats is minimized because the prestressed area is located according to known coordinates and held in place by a template. Further, no moving parts are used to create the weakened spot, fuse the end seal to the seed coat and cut away any excess material from the end seal, thereby ensuring increased reliability.
Thus, a method of attaching end seals to a manufactured seed, and the resulting manufactured seed, in accordance with the present invention has a high degree of reliability, is able to precisely locate and mass produce end seals and reliably attach the end seals to a seed coat, and minimizes the risk of damaging or contaminating the plant embryo during the process of manufacturing the seed.